THE CHAMBERS OF THE HEART. 741 
part. At the junction of the auricular and ventricular parts of this surface are 
the orifices of the pulmonary artery and the aorta, the former lying in front of 
the latter. ; 
The right margin of the heart consists of an upper auricular part and 
a lower ventricular part. The former is almost vertical; it les behind 
the cartilages of the third, fourth, fifth, and sixth ribs on the right side 
about half an inch from the margin : 
of the sternum; it is in relation with 
the right pleura and lung, the phrenic 
nerve with its accompanying vessels 
intervening, and it is marked by a 
shallow groove—the sulcus terminalis 
—which passes from the front of the 
superior vena cava to the left of the 
inferior vena cava. The lower part 
of the right margin (margo acutus) 
is sharp, thin, and usually concave, 
corresponding with the curvature of 
the anterior part of the diaphragm: 
it is formed by the right ventricle, 
and it lies almost horizontally in the 
angle between the diaphragm and the 
anterior wall of the thorax, passing 
from the sixth right costal cartilage 
behind the lower part of the body of 
the sternum, or the ensiform cartilage, 
and behind the cartilages of the sixth 
and seventh ribs on the left side to 
the apex of the heart. 
The left margin (margo obtusus) 
is formed mainly by the left ventricle, 
and only to a small extent by the left auricle. It is thick and rounded. It hes in 
relation with the left pleura and lung, the phrenic nerve and its accompanying 
vessels intervening, and it passes from just above the third left costal cartilage, about 
an inch from the sternum, to the apex of the heart, descending obliquely and with 
a convexity to the left. 
a 
Fic. 547.—TuHe RELATION OF THE HEART TO THE 
ANTERIOR WALL OF THE THORAX. 
I, II, II, IV, V, VI, the upper six costal cartilages. 
THE CHAMBERS OF THE HEART. 
Auricles (auricula cordis).—The auricular or basal portion of the heart is 
cuboidal in form. Its long axis, which lies transversely, 1s curved, with the con- 
cavity of the curve forwards. It is divided into two chambers—the right and 
left auricles—by a septum which runs from the front backwards and to the right, 
so obliquely that the right auricle lies in front and to the right, and the left auricle 
behind and to the left. 
Each auricle is also somewhat cuboidal in form, the long axis of the right 
auricle, however, being directed antero-posteriorly, whilst that of the left auricle 
lies vertically, and each chamber possesses a well-marked, ear-shaped, forward 
prolongation, which projects from the anterior and upper angle and is known as 
the auricular appendix. 
The right auricle. (atrium dextrum) receives, posteriorly, the superior vena cava 
above and the inferior vena cava below. Between these, and a little above its 
middle, it is crossed posteriorly by the lower right pulmonary vein. It is continuous 
below and in front with the right ventricle at the auriculo-ventricular aperture. 
Above and in front it is in relation with the ascending aorta, and from the junc- 
tion of this aspect with the right lateral boundary the right auricular appendix 
is prolonged forwards. On the right side it forms the upper portion of the right 
margin of the heart, and is in relation with the right phremic nerve and its accom- 
panying vessels, and with the right pleura and lung, the pericardium intervening. 
ery . 
7 
~ F) a. 
